Radiological imaging is recognized to have significant value for the dental practitioner, helping to identify various problems and to validate other measurements and observations related to the patient's teeth and supporting structures. Among x-ray systems with particular promise for improving dental care is the extra-oral imaging apparatus that is capable of obtaining a contiguous panoramic radiograph of the patient showing the entire dentition of the jaw. To obtain this type of image, a radiation source and an imaging detector, maintained at a fixed distance from each other, synchronously revolve about the patient, taking a series of images by directing and detecting radiation that is directed through the patient at different angles of revolution.
Combination systems that provide both CT and panoramic x-ray imaging have been proposed. For example, U.S. Pat. No. 6,118,842 entitled “X-RAY IMAGING APPARATUS” to Arai et al. discloses an X-ray imaging apparatus for both CT imaging and panoramic imaging. The apparatus includes an X-ray source, an X-ray detector for detecting X-rays having passed through the subject, and supporting means for supporting the X-ray source and the X-ray detector so that they are spatially opposed to each other across the subject; and mode switching means for switching between a CT mode and a panorama mode. To detect X-rays, only one large area X-ray detector is used. The X-ray imaging apparatus can obtain both types of images by switching modes during the imaging session. However, the proposed imaging apparatus performs both CT and panoramic imaging using only one detector. This requires an expensive detector capable of carrying out both imaging functions in a satisfactory manner.
More recently, U.S. Pat. No. 7,236,563 entitled “COMBINED PANORAMIC AND COMPUTED TOMOGRAPHY PHOTOGRAPHING APPARATUS” to Sa et al. describes a combination system that allows both CT and panoramic imaging using two separate sensors or detectors. By way of example, FIG. 1 in the present application shows an embodiment of the Sa et al. '563 imaging system, a combined panoramic and CT imaging apparatus 40. A column 18 is adjustable for height of the subject. The patient 12 or other subject, shown in dotted outline, is positioned between an x-ray source 10 and an x-ray imaging sensor panel 20. X-ray imaging sensor panel 20 rotates on a rotatable mount 30 in order to position either a CT or a panoramic sensor 121 for obtaining the exposure. For CT imaging, CT sensor 121 is positioned behind the subject, relative to x-ray source 10. The operator rotates CT sensor 121 into this position as part of imaging setup Similarly, the operator rotates panoramic sensor 121 into position behind the subject as part of the setup for a panoramic imaging session.
Another recent system combines CT, panoramic, and cephalometric imaging from a single apparatus. U.S. Pat. No. 7,424,091 entitled “COMBINED PANORAMIC, CT (COMPUTED TOMOGRAPHY) AND CEPHALOMETRIC PHOTOGRAPHING APPARATUS” to Park et al. describes such a system.
An imaging apparatus for extra-oral imaging and for imaging of teeth, bone, and various other structures of the patient's head should have some adjustability for the height of the patient. Referring to the example of FIG. 1, column 18 should be readily adjustable so that the same equipment can be used for adults or children of various heights. While height adjustment can be performed manually, there are advantages to adjustment methods that provide some amount of automation or at least mechanical assistance. In order for this capability to be provided, it is useful to have some way to measure column height. This not only serves to help automate the adjustment process, but also provides data that make it easier to repeat an imaging exam using similar parameters.
Various types of solutions have been proposed for determining the height of a telescoped column or of a component that moves up or down a column. Various types of limit switches could be employed to provide some level of information on height setting. However, limit switches can provide only range information rather than actual height. Rotary encoders and similar devices have also been proposed for obtaining height values, but may not be compatible with the mechanical actuators used.
Thus, there is a need for measurement apparatus for column height of an extra-oral imaging apparatus.